由文字生成path后制作写字的动画

在看以下这个开源组件的时候，发现一个非常棒的方法，能够将文字生成path，这样就能够作出用笔写字的效果了。

关键代码：

-(CGPathRef)pathRefFromText
{
    NSAttributedString *attributed = self.attributedText;
    
    CGMutablePathRef letters = CGPathCreateMutable();
    CTLineRef line = CTLineCreateWithAttributedString((__bridge CFAttributedStringRef)attributed);
    CFArrayRef runArray = CTLineGetGlyphRuns(line);
    for (CFIndex runIndex = 0; runIndex < CFArrayGetCount(runArray); runIndex++)
    {
        CTRunRef run = (CTRunRef)CFArrayGetValueAtIndex(runArray, runIndex);
        CTFontRef runFont = CFDictionaryGetValue(CTRunGetAttributes(run), kCTFontAttributeName);
        
        for (CFIndex runGlyphIndex = 0; runGlyphIndex < CTRunGetGlyphCount(run); runGlyphIndex++)
        {
            CFRange thisGlyphRange = CFRangeMake(runGlyphIndex, 1);
            CGGlyph glyph;
            CGPoint position;
            CTRunGetGlyphs(run, thisGlyphRange, &glyph);
            CTRunGetPositions(run, thisGlyphRange, &position);
            
            CGPathRef letter = CTFontCreatePathForGlyph(runFont, glyph, NULL);
            CGAffineTransform t = CGAffineTransformMakeTranslation(position.x, position.y);
            CGPathAddPath(letters, &t, letter);
            CGPathRelease(letter);
        }
    }
    
    UIBezierPath *path = [UIBezierPath bezierPathWithCGPath:letters];
    CGRect boundingBox = CGPathGetBoundingBox(letters);
    CGPathRelease(letters);
    CFRelease(line);
    
    
    [path applyTransform:CGAffineTransformMakeScale(1.0, -1.0)];
    [path applyTransform:CGAffineTransformMakeTranslation(0.0, boundingBox.size.height)];
    
    
    if (self.reversedAnimation) {
        return [[path bezierPathByReversingPath] CGPath];
    }
    
    return [path CGPath];
}